1. Field of the Invention
The present invention relates to fluid actuated shift bar housing assemblies for change gear transmission, and, in particular, relates to fluid actuated shift bar housing assemblies wherein selectively applied fluid pressure is effective to urge all of the shift bars into a neutral axial position, or to urge a selected one of the shift bars into at least one selectable axially displaced position for engaging a selected transmission gear ratio. More particularly, the present invention relates to a fluid actuated shift bar housing assembly, preferably actuated by a compressible fluid such as compressed air or the like, having a plurality of shift bars each having an axially centered position, a first axially displaced position wherein the shift bars are axially displaced from the centered position in a first axial direction and a second axially displaced position wherein the shift bars are axially displaced from the centered position in a second axial direction. The housing assembly associated with each shift bar has an actuating portion comprising three selectably pressurized chambers for urging said shift bars into any one of the three selectable axial positions thereof. A relatively small volume chamber is utilized to urge the shift bars positively into the axial centered positions thereof whereby a single valve may be utilized to pressurize the centering chambers for all of the shift bars of the shift bar housing assembly.
2. Description of the Prior Art
Shift bar housing assemblies wherein a plurality of axially moveable shift bars, also known as shift rails and shift rods, each carrying or associated with a shift fork, are selectively axially moved to engage or disengage a selected transmission gear by axial movement of a clutch member, or of a gear carrying clutch teeth, are well known in the prior art, as may be seen by reference to U.S. Pat. Nos. 3,105,395; 3,611,823; 4,152,949; 4,194,410 and 4,445,393, all assigned to the assignee of this invention and all hereby incorporated by reference.
Fluid actuated shift bar housing assemblies, usually actuated by pressurized hydraulic fluid or pressurized air, and the controls therefor, are also well known in the prior art, as may be seen by reference to U.S. Pat. Nos. 2,924,111; 2,931,237; 2,932,371; 2,943,502; 2,943,719; 2,974,766 and 4,445,393, all assigned to the assignee of this invention and all hereby incorporated by reference.
While the prior art fluidly actuated shift bar housing assemblies are generally satisfactory and are presently widely utilized, usually for remotely controlled and/or automatically controlled change gear transmissions, the prior art assemblies were not totally satisfactory as they were complicated and/or expensive to produce, install and/or service, and/or utilize springs or other means to center the shift rails in a neutral position which means tended to shift the transmission into neutral in the event of a loss of pressurized fluid which might undesirably render the driven device totally unusable and/or the volume of pressurized fluid required to actuate the neutral or centering cylinders of the various shift rods was relatively large requiring a relatively long time to exhaust and/or requiring a plurality of valves to be utilized to urge all of the shift bars to the axially centered position, thereby rendering the shift bar housing assembly undesirably unresponsive, complicated and/or expensive.